1. Field of the Invention
The present invention is directed generally to wireless communication systems.
2. Description of the Related Art
The terms roaming and mobility are typically used synonymously to refer to the general concept of a wireless subscriber being able to move around on a network instead of being chained to a single location. Starting from a high-level perspective, the specific functionalities related to how and where a user may roam are primarily determined by (1) ownership of the network, (2) the technology used by the network, (3) network attachment mechanisms (i.e., the means by which a user stays attached or re-attaches to the network), and (4) what type of service(s) must be supported during network re-attachment. By applying different requirements and definitions to the above criteria, one can create different contexts in which the commonly used terms “roaming,” “mobility,” and “handover” have different meanings.
There are two distinct classes of functionality involved when a roaming user moves from a first network into a second network. The first class of functionality is called administrative roaming and involves functionality related to the authentication model, credentials, billing, and cross authentication between the network operators. The second class of functionality is called network roaming and involves functionality related to network handover/re-attachment, whether the application sessions are maintained, and whether the network connectivity is broken or seamless (e.g., whether the internet protocol (“IP”) connection is maintained).
“Horizontal” handover roaming refers to the technical ability to handover from one base station to another within the same technology (e.g. from WiMAX to WiMAX, WiFi to WiFi, and the like). “Vertical” handover roaming refers to the technical ability to handover between base stations using two different types of technology (e.g., from WiMAX to WiFi, 3G to WiMAX, and the like). Many technical issues make vertical roaming difficult. In fact, many of these technical issues relate to horizontal roaming between different operators using the same technology. These technical issues include what happens when a user roams onto a network having Quality of Service (“QoS”) offerings that are different from (higher or lower than) the QoS offerings of the network to which the user was previously connected, how to navigate varying qualities of service, and perhaps most difficult of all, how to navigate different roaming policies and prices.
Mobility is generally defined as maintaining an ongoing data session during a change in a user's device point of attachment (base station or access point) to the radio network. Mobility may be broken down into two types: micro-mobility (Layer 2 mobility) and macro-mobility (Layer 3 mobility). Layer 2 and Layer 3 refer to layers of the Open Systems Interconnection Basic Reference Model (also referred to as the OSI Reference Model, OSI Model, and OSI seven layer model). The OSI Reference Model is a layered, abstract description of communications and computer network protocol design. Within this model, Layer 2 (“the data link layer”) responds to service requests from Layer 3 (“the network layer”), which is also referred to as the IP layer, and issues service requests to Layer 1 (“the physical layer”).
Micro-mobility is the simplest form of mobility and essentially involves handoffs between radio base stations belonging to a single Layer 2 Access Service Network (“ASN”). Layer 2 transfers data between adjacent network nodes in a wide area network (“WAN”) as well as between nodes on the same local area network (“LAN”) segment. Ethernet for local area networks is an example of a data link layer protocol. Within Layer 2, data link layer addresses, such as MAC addresses are used to route data between nodes. Layer 3 is responsible for end-to-end (source-to-destination) packet delivery, whereas the data link layer is responsible for node-to-node (hop-to-hop) frame delivery. Layer 3 is referred to as the Internet layer in the TCP/IP reference model. Within Layer 3, network layer addresses, such as IP addresses are used to route data between a source and a destination.
Within an ASN, the user is assigned an IP address that does not change as the user moves from one base station to another. However, the user's data link layer address does change as the user moves from one base station to another. Since the user's IP address does not change, the user's network applications/services are affected only by the speed at which the mobile station and base station can negotiate the Physical Layer/Media Access Control (“PHY”/“MAC”) aspects of the handover.
Macro-mobility often refers to an inter-ASN handover which occurs when a user moves across the service edge of one Layer 2 network into another Layer 2 network. This occurs when two ASNs are geographically adjacent to one another, and the user's connection is transferred from a first base station belonging to a first ASN to a second base station belonging to a second ASN. Typically, after such a handover, the user is attached to a network serviced by a different Layer 3 router. How the handover is effected dictates the impact to the user's network service. Generally, after the handover, the user has a new IP address, which causes connection oriented network applications and services to terminate.
Macro-mobility scenarios typically include both administrative and network roaming complexities. A wireless subscriber service area may involve movement between two networks that fall under the ownership/administration of completely distinct organizations (e.g., ISPs). For example, within a wireless subscriber service area, one base station may be operated by carrier “A” and a second base station operated by carrier “B.” The two networks must collaborate to complete the handoff and conduct authentication, authorization, and accounting (“AAA”) activities between the networks. These arrangements are similar to efforts in the voice-centric cellular industry that have been developed over many years.
Micro-mobility and macro-mobility are typically facilitated via radio architectures that allow a data session (or call) to be continued as a subscriber moves or transitions from one base station to another. At the radio architecture level, there are many mobility management parameters and functions that dictate the level of performance experienced by both the user and the network during the transition. Typical mobility management functions include the following:                Basic RF Configuration Parameters (frequency, bandwidth, channel maps);        RF scanning mechanisms;        Initial network entry, Idle mode, Handover, and network re-entry functions;        Network Information, such as Net ID, Net configuration, Neighbor lists;        Cell/Sector Reselection Algorithms;        Radio Resource Management (RRM) and Control (RRC);        Association/Registration/Authentication;        Paging Control;        Data Path functions; and        IP address allocation.        